Two methods are known for setting a precise target fill level inside a container during filling. These are: the Trinox method and the vacuum filling method. Common to both methods is that a pipe-shaped probe is used on the filling element to determine fill level. The probe includes a gas-return pipe and extends into the container during the filling with at least one lower probe-opening. In both methods, the container is initially overfilled so that, during a filling phase, the lower probe-opening is submerged below the filling material level. After the filling phase, which ends with the closing of the liquid valve of the filling element, a fill-level correction phase begins. During this phase, overfilled filling material is removed from the container through the probe and returned to the filling-material tank.
In the Trinox method, to remove the overfilled filling material in the fill level correction phase, a sterile inert gas, for example CO2, at a pressure lying above the filling pressure or the pressure prevailing in the filling-material tank, is released into a headspace of the container. This pressure forces filling material through the probe back into the filling material tank until the probe opening is outside the filling material. At this point, the target fill level is reached. A disadvantage of the Trinox method, therefore, is the additional costs due to the inert gas.
In vacuum filling, which is mainly used in the filling of still products, i.e. for filling products that do not contain CO2, a negative pressure prevails in the filling-material tank. After closing the liquid valve, the container is removed from its sealed seat or sealed position on the filling valve so that, in the fill-level correction phase, the filling material is returned, by suction through the probe, into the filling-material tank due to the pressure difference between the pressure in the filling-material tank and the pressure of the ambient air until the probe opening is outside the filling material and thus the target fill level is reached.
A disadvantage of the vacuum filling method is that ambient air, and with it also possibly dirt, microorganisms, and pathogens, such as mold, and bacteria, inevitably enters the container's headspace and is thus placed into contact with the filling material.